Axial flow fan



J. G. SAWYER AXIAL FLOW FAN April 8, 1952 3 Sheets-Shes; 1

Filed Aug. 22, 1946 INVENTOR. j; I I

ATTORNEY April 8, 1952 J. G. SAWYER 2,592,471

AXIAL FLOW FAN Filed Aug. 22, 1946 3 Sheets-$119 2 A TORNEY April 3,1952 J. G. SAWYER 2,592,471

AXIAL FLOW FAN Filed Aug. 22, 1946 3 Sheets-Sheet 3 L 11 45. gcm, z!

ATTORNEY Patented Apr. 8, 1952 UNITED STATE PATENT OFFICE]:

This invention relates to certain new and useful improvements in fans orblowers of the axial flow type designed to produce a current of air orother fluid or to produce a pressure rise.

The capacity, or the ability of fans of this type to do work, dependsupon two factors, that is, the difference in pressure between the inletand outlet pressures of the fan, represented by the symbol Ap and theaxial speed of flow (in cubic feet per second) of the gas delivered,represented by the symbol Q. The pressure difference obeys the followingequation:

Ap= oNDr (1) where t is a dimensionless coefficient called the pressurecoefiicient, p is the density of the gas, N is the frequency ofrevolution of the fan runner, and D is the outside diameter of the fanrunner. The flow of the gas delivered obeys the equation:

where o is another dimensionless coeflicient called the flowcoeflicient. It is easily apparent that, for a given size fan and agiven rotational speed, the greatest capacity for work and the highestpressures are secured with fans having relatively high pressure and flowcoeflicients. In addition, the developed pressure obviously variesdirectly with the pressure coefiicient. Both pressure and fiowcoefficients depend principally upon the shape, configuration andposition of the fan blades, so that the proper design of the fan bladesis a factor of the utmost importance in securing high pressures and highcapacities.

One of the objects of the invention is to provide a fan of thischaracter which is so designed and constructed as to develop maximumcoefllcients of pressure and capacity at minimum speeds and with aminimum of noise, and wherein the fan blades are so spaced and curved onthe stream filament principle to develop pressure coeflicients of theorder of unity and higher.

Another, object is to provide a motor-driven axial flow fan which isdesigned to take the boundary layer air from the surfaces of the partsand direct it into the path of the motor to effectually cool it andimprove the difiusing action of the fan.

Other features of the invention reside in the construction andarrangement of parts hereinafter described and particularly pointed outin the appended claims.

In the accompanying drawings: Figure 1 is a sectional elevation view ofthe fan embodying my:

invention. Figure 2 is a top plan view of one of the fan blades. Figure3 is an end view thereof. Figure 4 is a sectional side view of one ofthe blades showing the manner of mounting the same. Figures 5, 6, and 7are horizontal sections taken on the correspondingly numbered lines inFigure 4. Figure 8 is a top plan view of one of the guides or vanes.Figure 9 is an end view thereof. Figure 10 is a cross section taken online Ill-Ill, Figure 9. Figures 11, 12, and 13 are schematic profileviews, with vector diagrams, of various f an blade sections and guidevane sections. Figures 14 and 15 are geometrical drawings showing themethod of developing the fan blade and aft vane profiles and contours.

Similar characters of reference indicate corresponding parts throughoutthe several views.

In accordance with the present invention Iha-ve discovered a principlein the design of axial flow type fans, whereby pressure coeflicientsof-tl'ife order of unity and above. may be developed with efficienciesabove those heretofore obtained? obtaining these results I have found itnecessary to so design the blade curvature and its thickness so as toaccomplish most of the turningorth'e fluid medium and develop most ofthe pressure in the early stages of the interblade fluid passage; thatis, most of the work is done upon the'fluid in the inlet or up-streamportion of the blade.

In this type of fan, the blades act to guide or direct the flow of airthrough the runner section. This is known as the laminar flow or streamfilamen principle. By curving the fan blades, the air which initiallyenters the runner section in a direction opposed to the direction ofmotion of the fan blades, is caused to flow in laminar along a curvedpath roughly parallel to the walls defined by two adjacent fan blades,and to leave the runner section in a diiIerent direction.

The discharge guide vanes are also curved and they serve to transformany residual rotational component of fiow of the air as it leaves thetan section into axial flow. In designing a fan for commercial use, thedesired pressure differential, the desired volume of air flow, thenumber of revolutions per minute, the density of the air, and the spaceavailable, including the fan diameter and thickness, are usuallypresented to the designer as conditions for which the fan is to bedesigned. From these design conditions, the pressure coeflicient 1,0 isobtained from equation (1) above. If the pressure coefiicient thuscalculated proves to be higher than is theoretically or practicallyobtainable, it

is then impossible to design a fan which willmeet the design conditions.As pressure coefflcients up to '3 and above with good efficiency areobtainable with the fans of my invention. it is evident that it ispossible to satisfy much more exacting design conditions than wereheretofore possible.

Having determined that it is possible to attain the calculated pressurecoefficient, the next step is to calculate the required angles of thefan blades and uide vanes, if the latter are used. The curvature of thefan blades imparts to the air stream passing through the runner sectiona change in component of absolute rotational velooity designated as ACu.The value of A014 is determined by the design conditions, according tothe following equations:

where 1 is the efficiency of the fan (assumed to be .75) or otherreasonable value, determined according to experience and u is the speedof the fan blade tips (equal to TI'ND). ACu, however, increases with theangle of air turn hi (assumed at the present stage to be equal to rs),as that the pressure diiferential Ap obtainable depends upon the anglethrough which the air can be turned.

In the preferred embodiment of this invention, guide vanes, either inletor aft vanes or both, depending upon the particular installation areemployed. With this construction, the air leaves .the fan in an axialdirection and the work done in turning the air manifests itself as arise in pressure. The runner blades are set at the angle 1, which iscalculated according to the vector diagrams shown .in Figures 11, 12, 13depicting forms of the invention employing inlet vanes 29 only in Figure11, aft vanes 2| only in Figure 12, and both inlet and aft vanes inFigure 13, .in combination with fan runner blades 22. In these diagrams,the symbol Cm represents axial velocity, and W1 and W2 the airvelocities relative to the fan blades at the inlet and outlet ends, re-

spectively, of the runner section, while the remaining symbols are aspreviously indicated. The value of Cm is expressed in linear measure persecond and is equal to Q 1r(D d Accordingly, since the values of Cm, ACuand u are determined from the design conditions, it is a relativelysimple matter to calculate the angles c1 and re, and the values of an(equal to 1b), W1 and'Wz if desired.

Having determined these angles, the camber line of the blade is nextfixed and reference is had to Figure 14 wherein lines 23 and 24represent the inlet and outlet planes, respectively, of the fan runner,and the distance between them is fixed by the design conditions. A line25 is erected perpendicular to line 23 and a line 26 drawn through theintersection of 23 and 25 in such a fashion that the angle between 25and 28 is equal to 51. The object is to then draw a camber line curve'21 tangent to 28 at the point of intersection with 23 and intersectingline 24 at an angle of '902, and such that the change of length S Where,It and K are positive constants.

Letting a=cZa/ds, these constants are expressed as follows:

/L2//L1=.70 approx.

and

.is determined at one point. I have found that it increases with R, andthat the ratio varies somewhat from linearity. I have also found thatoptimum conditions are secured when R/a varies linearly fromapproximately 3 at the inlet to 4 at the outlet. In any case, havingselected the values of R/a, it is easy to determine the blade pitch orblade spacing b from the following equation:

a=b cos (9T) ('7) where T is the thickness of the blade section. At theleading or trailing edge, 0 is the equal to 01,

or 02, respectively, a=3R or 4R respectively, and,

T is equal to 0. From the latter, b is determined throughout, and thevalue of -1' throughout the range is then determined from Equation 7.

Referring now to Figure 15, the value of r is calculated with referenceto each particular point on the camber line 21, according to Equation 7.It is plotted at any point by erecting a perpendicular 28 to the camberline at a particular point 29 on such line, and laying off a distance/21' on each side of the camber line. The loci of the points 30 and 3|at distances of /z'r from such camber line on the perpendicular line 28then determine the blade profile, having a convex side 32 and a concaveside 33.

The width a between adjacent blades may now be defined as follows, withreference to each particular point on the camber line 21. A line 34perpendicular to the line 28 is erected at the point 30, and a point 35on the camber line 36 of the adjacent blade is selected to be at thesame location of such line 36 as the particular point 29 is on the line27. A line 37 perpendicular to the line 36 is erected as before, and thepoint 38 laid off at a distance &1- from line 36. A line 39perpendicular to 31 at point 38 is erected, and the perpendiculardistance between lines 34 and 39 is defined as a.

After a single blade profile is plotted as described above, and a secondsimilar blade profile plotted from the similar camber line 36 at adistance b therefrom, the values of a with respect to S are checked atvarious points along the camher line, to see whether or not equations(4) and (5) hold. If these conditions are not satisfied, then the formof the camber line or the value of R/a have not been properly selected,and a different curve or a different value of R/a or both must beselected. Thus an ellipse of slightly different eccentricity or someother different curve may be tried. Again, the blade pitch b may bereplotted with lower values of R/a. Fi-

n'ally. the vaiue of b must-be such that-D1 lean integral multiple Mthereof, since it is-imposs'ible 'toconstruct a fan with a fractionalnumber of'blades.

The calculations as described above determine the blade profile at thetip. The profiles at other points inward of the tip aredeterm'ined in asimilar fashion. In place of the value, u (tip speed) in equation ('3')and thevector diagrams accompanying Figures '11, 1-2, and 13', asomewhat lesser value '21rNrm is used, where Tm is the radius of therunner section at the profile point tobe determined. This will result indifferent values of 01, 92, it etc., and consequentlydifierent bladeprofiles and'blade spacings. All profiles should as closely as' possiblesatisfy the con-di tlons previously described except that instead oib='1rMD, therelationshipb=21rMT1n should hold, where M obviously musthave the same value at all profiles. As profiles are determined nearerthe axis of the fan runner section, the deviations from the prescribedor assumed conditions may be sufiiciently great as to make itimpractical to proceed further. If it has not been determined otherwise,this will determine the value of d. When a sufiiciently representativenumber of blade profiles have been determined, they are combined into asmooth blade contour, the ends of the blade chords should preferably liein two smooth curves, and to accomplish this may require some adjustmentin their relative positions. A typical such blade construction (for afan having runner" section and aft vanes only) is illustrated in Figures2 to 7 inclusive of the drawlngs. liiach blade 22 is detachably anchoredto the runner wheel of the fan and for thispurpose has a stud thereonseated in a companion socket 40 in the wheel and secured thereto byaboltdl.

If the inlet guide vanes are used, they should be curved so as to impartto the air a rotational component of absolute velocity opposite indirection to that imparted by the fan runner section. If the inlet guidevanes alone are used, the rotational component should preferably beequal in magnitude to that imparted by the fan runner section, in orderthat the air from the runner section may b delivered in an axialdirection. As the mean flow of the air entering the inlet guide vanes isin a straight line in an axial direction, uncomplicated by rotationalvelocity, the problem of inlet guide vane design is simply only of .ductdesign, to turn the air through the required angle. At the inlet side ofthe inlet guide vanes, therefore, the walls of the vanes should beparallel to the direction of flow or perpendicular to the inlet plane ofthe vanes. In the form shown in Figure 11, the angle 6'0 at the outletof the inlet guide vanes is determined by the equation The perpendiculardistance between the inlet and outlet planes of the inlet guide vanes isa design condition. It is suflicient to build the vanes out of ordinarysheet metal, tapered at the inlet and outlet edges to secure streamlinenow. They are bent simply to form a contour Whose profile is a segmentof a circle. The chord spacing ratio need not be as high as in the caseof the fan b1ades,but is preferably at least 0.75..

If aft vanes or discharge guide vanes are used, they should also becurved so as to impart to the air a rotational component of absolutevelocity opposite "in direction to that'imparted .by'theian runnersection. If art vanes :alone are'nsed the rotational component shouldpreferably :be equal in magnitude to that imparted by the :fanrunnersection, in order that the "air .from the aft'vanes may be delivered inan axial direction. the inlet guide vanes, however, the contour shouldbe developed in a fashion similar'to that employed for the fan bladesproper, except that the direction of curvature is opposite. The inletangle 93 is negative .and .is determined from the vector diagram, asshown in Figures .12 and13 while the outlet angle (24 is theoreticallyzero, since the flow at this point should be :axial. .In practice,however, the air turn is not .quite :as great as the blade turn, so thatthe outlet angle at is slightly positive. usually about 5 degrees.Having determined the angles 03 and 04, the camher line, blade profile,and blade contour are determined in exactly the same fashion as for thefan blades proper. The chord-pitch ratio should be of the same order ofmagnitude as in the case of the fan blades proper. A typicalconstruction, for use in combination with the fan blades illustrated inFigures 2 to 7 inclusive, is illustrated in Figures 8 to 10 inclusive.

In most installations, either inlet guide vanes or aft vanes are used.It is usually preferred, however, not to use both inlet and aft vanes,because of space limitations and because the mathematical calculationsrequired are more involved. Nevertheless, under certain conditions,particularly where extremely high pressures are desired,

both inlet and aft vanes may be used. .Such a structure is illustratedin Figure 13.

Referring now to Figure 1, this illustrates-a conventional structureembodying my invention, in which a fan of the blade and vane arrangement shown in Figure 12 is employed. The fan is installed in aduct 42,the runner section 43 with its blades 22 being drivenrby an electricmotor M, in the direction indicated by the small arrows. The Lian blades22 and the aft guide vanes 21 are designed as hereinbefore indicated,the combination serving to force the air through the duct in thedirection indicated by the large arrow.

While the invention has been generally described With reference to fans,I have found that the principle of my invention is particularlyapplicable to compressors where economy of space is a primeconsideration. Hitherto, axial flow blowers have not ordinarily beenused as compressors because of the low pressure coemcients available,but with my invention, two or more runner sections may be advantageouslyand obviously combined on a common shaft, to form a multi-stagecompressor.

The described method of determining blade profile results in theaccomplishment of most of co the fluid turning and diffusion in theearly part of the blade passage, where the boundary layer is small, andflow conditions are more favorable. A more generous R/a and a lower rateof diffusion old/(is are employed toward the outlet where the boundarylayer conditions are less favorable. Then this portion of the blade isless taxed. This method will reduce losses to, a minimum, and as testshave indicated, higher efiiciencies are obtainable.

For the purpose of effectually cooling and improving the diffusingaction of the fan, the boundary layer air is directed into the path oftheemotor, the air circulating from the ductv 42 being directedv intoone end of the motor housing 45 and out of its opposite end, air intakeports having a plurality of blades thereon spaced to define fixedpassages therebetween, a stationary guide section disposed in said ductin axiallyspaced adjacent relation to said runner section and having aplurality of vanes thereon spaced to define fixed passages therebetween,the runner blades being curved to form a concave advancing face and aconvex retreating face with respect to the direction of rotation of saidrunner section and said guide vanes being curved with their convexityand concavity opposed to the convexity and concavity of said blades, therate of change of width of the passage between adjacent blades withrespect to the change of length of the blades camber line being reducedlinearly from its initial value at the blades leading edge to 70% ofsaid initial value at the blades trailing edge, and the ratio of theblades camber line radius to the width of the passage between bladesvarying linearly from approximately 3.0 at the leading edge toapproximately 4.0 at the trailing edge.

2. An axial flow blower, means forming a duct, a rotatable runnersection disposed therein and having a plurality of blades thereon spacedto define fixed passage therebetween, a stationary inlet guide sectiondisposed in said duct in axially-spaced adjacent relation to said runnersection and having a plurality of vanes thereon to define fixed passagestherebetween, the runner blades being curved to form a concave advancingface and a convexing retreating face with respect to the direction ofrotation of said runner section and said vanes being curved with theirconvexity and concavity opposed to the convexity and concavity of saidblades, and the rate of change of width of passage between adjacentblades with respect to change of length of the blades camber line beingreduced linearly from its initial value at the blades leading edge to70% of said initial value at the blades trailing edge, and the ratio ofthe blades camber line radius to the width of blade passage varyinglinearly from approximately 3.0 at the inlet to approximately 4.0 at thetrailing edge.

3. An axial flow blower, comprising means forming a duct, a rotatablerunner section disposed therein and having a plurality of blades thereonspaced to define fixed passages therebetween, a stationary aft guidevane section disposed in said duct in axially-spaced adjacent relationto said runner section and having, a plurality of vanes to define fixedpassages therebetween, the runner blades being curved to form a concaveadvancing face and a convex retreating face with respect to thedirection of rotation of said runner section and said vanes being curvedwith their convexity and concavity opposed to the convexity andconcavity of said blades, and the rate of change of width of passagebetween adjacent blades with respect to change of length of the bladescamber line being reduced linearly from its initial value at the bladesleading edge to '7 of said initial value at the blades trailing edge,and the ratio of the blades camber line radius to the width of bladepassage varying linearly from approximately 3.0 at the inlet toapproximately 4.0 at the trailing edge.

4. An axial flow blower, comprising means forming a duct, a rotatablerunner section disposed therein and having a plurality of blades thereonspaced to define fixed passages therebetween, a stationary inlet guidesection disposed in said duct in axially spaced relation at one side ofsaid runner section and having a plurality of vanes thereon to definefixed passages therebetween, a stationary aft guide section disposed insaid duct in axially spaced relation at the other side of said runnersection and having a plurality of aft vanes thereon to define fixedpassages therebetween, said blades being curved to form a concaveadvancing face and a convex retreating face with respect to thedirection of rotation of said runner section and both sets of said vanesbeing curved with their convexity and concavity opposed to the convexityand concavity of said blades, and the rate of change of width of passagebetween adjacent blades with respect to change of length of the bladescamber line being reduced linearly from its initial value at the leadingedge of the blade to 70% of said initial value at the blades trailingedge, and the ratio of the blades camber line radius to the width ofblade passage varying linearly from approximately 3.0 at the inlet toapproximately 4.0 at the trailing edge.

5. An axial fiow fan, comprising means forming a duct, a rotatablerunner section disposed therein having blades thereon to define fixedpassages therebetween, a stationary inlet guide section disposed in saidduct in axially-spaced adjacent relation to said runner section andhaving vanes thereon, the blades being curved to form a concaveadvancing face and a convex retreating face with respect to thedirection of rotation of said runner section and the guide section vanesbeing of opposing curvature to said runnerblades, and the rate of changeof width of passage between adjacent blades with respect to change oflength of the blades camber line being reduced linearly from its initialvalue at the leading edge to approximately 70% thereof at the trailingedge as-determined by the following formulas:

where k and K are positive constants and letting #:da/dS, theseconstants are expressed as m/m .70 approximately.

6. An axial flow fan, comprising means forming a duct, a rotatablerunner section disposed therein having blades thereon to define fixedpassages therebetween, a stationary inlet guide section disposed in saidduct in axially-spaced adjacent relation to said runner section andhaving vanes thereon, the blades being curved to form a concaveadvancing face and a convex retreating face with respect to thedirection of rotation of said runner section and the guide section vanesbeing of opposing curvature to said runner-blades, and the rate ofchange of width of passage between adjacent blades with respect tochange of length of the blades camber line being reduced linearly fromits initial value at the leading edge to approximately 70% thereof atthe trailing edge as determined by the following formulas:

9 where k and K are positive constants and lettin zda/ds, theseconstants are expressed as KS2 I*2/I 1 [lg/#1 .70 approximately, and theblade spacing being determined, after having selected the radius ofcurvature value R/a. Irom the following formula:

(1:18 cos (ti-r) 7. An axial flow fan, comprising a rotatable runnersection having blades thereon, a stationary inlet guide section havingvanes thereon, the blades being curved to form a concave advancing faceand a convex retreating face with and,

JAMES G. SAWYER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,958,145 Jones May 8, 19342,224,519 McIntyre Dec. 10, 1940 2,378,372 Whittle June 12, 1945

